Post deposition plasma treatment to increase tensile stress of HDP-CVD SIO2

ABSTRACT

A plasma treatment process for increasing the tensile stress of a silicon wafer is described. Following deposition of a dielectric layer on a substrate, the substrate is lifted to an elevated position above the substrate receiving surface and exposed to a plasma treatment process which treats both the top and bottom surface of the wafer and increases the tensile stress of the deposited layer. Another embodiment of the invention involves biasing of the substrate prior to plasma treatment to bombard the wafer with plasma ions and raise the temperature of the substrate. In another embodiment of the invention, a two-step plasma treatment process can be used where the substrate is first exposed to a plasma at a processing position directly after deposition, and then raised to an elevated position where both the top and bottom of the wafer are exposed to the plasma.

BACKGROUND OF THE INVENTION

One of the primary steps in the fabrication of modern semiconductordevices is the formation of a thin layer on a semiconductor substrate bychemical reaction of gases. Such a deposition process is referred togenerally as chemical-vapor deposition (“CVD”). Conventional thermal CVDprocesses supply reactive gases to the substrate surface whereheat-induced chemical reactions take place to produce a desired layer.Plasma-enhanced CVD (“PECVD”) techniques, on the other hand, promoteexcitation and/or dissociation of the reactant gases by the applicationof radio-frequency (“RF”) energy to a reaction zone near the substratesurface, thereby creating a plasma. The high reactivity of the speciesin the plasma reduces the energy required for a chemical reaction totake place, and thus lowers the temperature required for such CVDprocesses as compared to conventional thermal CVD processes. Theseadvantages are further exploited by high-density-plasma (“HDP”) CVDtechniques, in which a dense plasma is formed at low vacuum pressures sothat the plasma species are even more reactive. “High-density” isunderstood in this context to mean having an ion density that is equalto or exceeds 10¹¹ ions/cm³.

During a conventional chemical vapor deposition process, the substrateremains on the surface of the pedestal or support structure for theduration of the deposition and is then lifted off the pedestal by alifting mechanism for output from the chamber. The lifting mechanism maycomprise, for example, a servo-driven motor attached to a plurality oflift fingers which minimally contact the bottom surface of thesubstrate. In some deposition processes, particles on the backside ofthe substrate may be removed after the deposition process by lifting thesubstrate to an elevated position and exposing the substrate to a plasmato clean the substrate and remove backside contamination.

In a relatively newly developed method of enhancing transistorperformance, the atomic lattice of a deposited material is stressed toimprove the electrical properties of the material itself, or ofunderlying or overlying material that is strained by the force appliedby a stressed deposited material. Lattice strain can increase thecarrier mobility of semiconductors, such as silicon, thereby increasingthe saturation current of the doped silicon transistors to therebyimprove their performance. For example, localized lattice strain can beinduced in the channel region of the transistor by the deposition ofcomponent materials of the transistor which have internal compressive ortensile stresses. For example, silicon nitride materials used as etchstop materials and spacers for the silicide materials of a gateelectrode can be deposited as stressed materials which induce a strainin the channel region of a transistor. The type of stress desirable inthe deposited material depends upon the nature of the material beingstressed. For example, in CMOS device fabrication, negative-channel(NMOS) doped regions are covered with a tensile stressed material havingpositive tensile stress; whereas positive channel MOS (PMOS) dopedregions are covered with a compressive stressed material having negativestress values.

As tensile and compressive stresses are examples of internal loading,they may be regarded as positive and negative values, respectively, ofthe same type of normal loading. Thus, an unstressed material is neithercompressive or tensile. A material may progress from having acompressive stress to becoming more tensile and gradually exhibiting atensile stress depending on external factors, and vice versa.

Given the stresses created by depositing material on a substrate, it isdesirable to control the level of stress generated in the depositedmaterial, as well as change the level of stress after processing stepsare complete. A variety of different deposition parameters can controlthe stress level of a material during deposition, including temperature,and RF power levels among others. Additionally, various techniques havebeen developed to change the stress of a material already deposited overa substrate including exposure of the substrate to a plasma, exposure ofthe substrate to ultraviolet light or electron beams, and annealing thedeposited layer. Despite the availability of the above techniques, newmethods of changing the level of stress of a deposited layer aredesirable.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a method of forming a dielectric layerwhere the tensile stress of the deposited layer is increased by a plasmatreatment at an elevated position. The substrate is first positionedwithin the chamber and the dielectric layer is deposited upon thesubstrate, according to conventional methods. The substrate is thenraised above the substrate support and exposed to a plasma treatmentwhich increases the tensile stress of the deposited layer. The plasmacreated during deposition can be continually maintained throughout themovement step and raising of the substrate to an elevated position, orcan be extinguished and reformed during the plasma treatment step. In aspecific embodiment of the invention, the substrate is raised above thesubstrate support by a plurality of lift pins that extend the lift pinsthrough the substrate support.

The initially deposited layer can have a first stress which iscompressive, and after plasma treatment, have a second stress which istensile. In this case, the dielectric layer deposited may have a stressof less than 100 MPa compressive stress. Alternatively, the initiallydeposited layer can have a first stress which is tensile, and a secondstress after deposition which is more tensile than the first stress. Theincrease in tensile stress exhibited by the deposited layer after plasmatreatment can be 100 MPa or more.

The invention further describes a method of increasing the tensilestress of a layer on a substrate disposed on a substrate support in asubstrate processing chamber. The steps of this process include placingthe substrate in the chamber, positioning the substrate on the surfaceof the substrate support, depositing the layer of the substrate whereinthe deposited layer has a first stress as a result of deposition,raising the substrate above the surface of the substrate support to anelevated position, and while in the elevated position, exposing the topand bottom surface of the substrate to a plasma whereby the stress ofthe layer is increased to a second stress more tensile than the firststress. Ideally the first stress of the deposited layer is less than orequal to 100 MPa as a result of deposition, and the second stress of thedeposited layer after plasma treatment is 100 MPa more tensile than thefirst stress.

In an alternative embodiment of the invention, a sputtering process isincorporated after deposition of the dielectric layer, thus exposing thewafer to plasma bombardment that raises the temperature of the wafer. Abias is provided to the substrate which attracts the plasma ions towardsthe substrate at a greater velocity.

In another embodiment of the invention, a two-step plasma treatmentprocess can be used following deposition whereby the substrate isexposed to an initial plasma treatment at a processing position when theback surface of the substrate is still in contact with the substratesupport, and then raised to an elevated position for further treatment.

The plasma treatment process described within this invention may beparticularly suited for use within an shallow trench isolation (STI)process. In this process, an oxide layer and nitride layer are depositedon a substrate and patterned to form a trench opening. A trench is thenetched into the substrate, and the substrate is then transferred into achamber suitable for dielectric deposition. A dielectric layer is thendeposited over the substrate, filling the trench and covering the mesaregions adjacent to the trench. The substrate is then raised to anelevated position above the substrate support and exposed to a plasmawhich increases the tensile stress of the substrate. A sputteringprocess can also be implemented following deposition as well, inconjunction with the plasma treatment. The substrate is then removedfrom the dielectric deposition chamber, and portions of the dielectriclayer are removed so that the dielectric layer is at a vertical layereven with the topmost portion nitride layer. The nitride and pad oxidelayers are then removed to form the STI structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing an exemplary process flow used to increasethe tensile stress of a dielectric layer;

FIG. 2A is a simplified diagram showing the position of a substrate andlift pins in a loading position;

FIG. 2B is a simplified diagram showing the position of a substrate andlift pins in a lift position;

FIG. 2C is a simplified diagram showing the position of a substrate andlift pins in a processing position;

FIG. 3A is a simplified diagram of one embodiment of a high-densityplasma chemical vapor deposition system according to the presentinvention;

FIG. 3B is a simplified cross section of a gas ring that may be used inconjunction with the exemplary CVD processing chamber of FIG. 1A;

FIG. 4 is a flowchart showing an alternate process flow used to increasethe tensile stress of a dielectric layer using a sputtering processafter deposition;

FIG. 5 is a flowchart showing an alternate process flow used to increasethe tensile stress of a dielectric layer by using a two-step plasmatreatment process; and

FIGS. 6A-6E are a series of diagrams showing a typical process flow fora shallow trench isolation (STI) process.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for a method of increasing the tensilestress of a deposited layer on a substrate by treating the substratewith a plasma at an elevated position above the substrate support afterthe deposition process has concluded. A second embodiment of theinvention incorporates a sputtering process prior to plasma treatment bywhich the temperature of the substrate is increased by exposing thesubstrate to plasma ion bombardment prior to the plasma treatmentprocess. A bias voltage is provided to the substrate support whichattracts the plasma ions toward the substrate, thus causing the ions toimpact the top surface of the substrate and raise the temperature of thesubstrate. Another embodiment of the invention utilizes a two-stepplasma treatment process wherein the substrate is first exposed to aplasma at process position immediately following deposition. The plasmais maintained within the chamber during the movement step when thesubstrate is then raised to an elevated position, and both the top andbottom portions of the substrate are exposed to the plasma.

Semiconductor manufacturers have used various plasma treatment steps totreat dielectric layers deposited on a substrate for a variety ofdifferent reasons. Typically, such previously used plasma treatmentssteps expose the substrate to a plasma while the substrate is positioneddirectly on top of a substrate support at a processing (e.g., adeposition) position. Embodiments of the invention, however, expose thesubstrate and deposited dielectric layer to a plasma treatment processwhile the substrate is positioned above the substrate support. Thus,embodiments of the invention allow the plasma to contact at least aportion of the bottom surface of the substrate in addition to the topsurface. The inventors have found that such a technique can bebeneficially used to increase the tensile stress of a deposited layer.While not being limited to any particular theory, the inventors believethat exposing both the bottom and top surfaces of the substrate to theplasma enables thermal changes and/or phase shifts in the depositedlayer more easy to achieve due to the increased area of exposure to theplasma.

In order to better appreciate and understand the present invention,reference is made to FIG. 1, which is a flowchart depicting the stepsassociated with an exemplary embodiment of the invention, and FIGS.2A-2C, which are simplified cross-sectional views of a substrate supportand lifting mechanism contained within a substrate processing chamber.The lifting mechanism utilized within this embodiment of the inventionis a plurality of lift pins configured to position the substrate on thesubstrate support. The process discussed below with respect to FIGS. 1and 2A-2C is for plasma treatment of an undoped silica glass (USG) layerthat may be used, for example, in a shallow trench isolation (STI)application. It us to be understood however, that the techniques of thepresent invention are applicable to other applications such asintermetal dielectric (IMD) layers and premetal dielectric (PMD) amongothers. Also, techniques of the present invention are applicable to thedeposition of a variety of materials using HDP-CVD techniques. Thesematerials, the use of which is application specific, include dopedsilica glass films, such as phosphorous silica glass (PSG), boron-dopedsilicate glass (BSG), borophosphosilicate glass (BPSG) andcarbon-doped-silica glass (SiOC), silicon nitride, silicon oxynitride,silicon carbon materials (SiC) and others.

An example illustrating the operation of such lift pins is shown in FIG.2A-2C, where the various components are not shown to scale. The liftpins 92 are adapted to position the substrate 90 in any one of threepositions relative to the substrate receiving portion 19. The lift pins92 may reside within the chambers 93 and be driven with a motor (notshown) such that the three positions are achieved by moving the liftpins 92 out from or into the substrate receiving portion a specificdistance. In a first position, shown in FIG. 2A, the lift pins 92 arepositioned such that the substrate 90 can be received from the robotblade at the upper loading position 57. The upper loading position 57 isdetermined so as to be convenient for receiving the substrate 90 fromthe robot blade. In a second position, the lift position 58 shown inFIG. 2B, the lift pins 92 are further recessed into the substratereceiving portion 19 and positioned so that the substrate 90 is not incontact with the substrate receiving portion 19. The distance betweenthe substrate 90 and the substrate receiving position 19 at liftposition 58 can be varied depending on the process used, so long as thesubstrate 90 and substrate receiving portion 19 are not in contact. In athird position, shown in FIG. 2C as the processing position 56, the liftpins are positioned below the top surface of the substrate support sothat the substrate 90 is in contact with the substrate receiving portion19, where it may be electrostatically chucked into a secure position forprocessing.

Referring now to FIG. 1, at step 200, the substrate 90 to be processedis transferred into the substrate processing chamber and received at theupper loading position 57, resting on the lift pins 92. At step 210, thesubstrate 90 is then moved to a processing position 56 by retracting thelift pins 92 so that the back surface of the substrate 90 rests on thesubstrate receiving portion 19 at a processing position 56, as shown inFIG. 2C. The substrate 90 is now ready for deposition.

In one embodiment of the invention, the process conditions for thedeposition step 220 are selected so as to deposit a dielectric layerhaving an as deposited stress level of between 100 MPa compressivestress (a relatively low compressive stress level) to 50 MPa tensilestress. The inventors have found that exposing dielectric layers havingas-deposited stress levels within this range results in a substantialchange in the absolute stress level of the dielectric layer (a change ofat least 100 mPa in some embodiments and a change of at least 150 MPa incertain other embodiments). According to some embodiments of theinvention the plasma treatment described herein is most effective ifused on a deposited layer with an initial stress of 0-50 MPa compressivestress or 0-50 MPa tensile stress (i.e., an as-deposited stress ofbetween 50 MPa compressive and 50 MPa tensile).

In contrast, many conventional HDP-CVD deposition methods used todeposit a silicon oxide layers for use as dielectric material inintegrated circuits commonly produce relatively highly compressivestress layers of greater than 150 MPa compressive stress. The inventorshave found that plasma treatment of dielectric layers having suchrelatively high compressive stress results in a considerably reducedchange in the absolute stress level than if the dielectric layer has anas-deposited stress level within the ranges described above and thuscannot alter the stress level of the layer by a sufficient enough amountto reach the tensile stress levels desirable in some applications.

As would be understood by a person of ordinary skill in the art, severalparameters of the deposition process used in step 220 can be alteredfrom values used in conventional HDP-CVD processes to deposit a siliconoxide layer having an as-deposited stress level within the desired 100MPa compressive stress (a relatively low compressive stress level) to 50MPa tensile stress. For example, the deposition parameters used in step220 may differ from the parameters used in a conventional HDP-CVD STIprocess by using one or more of a lower substrate temperature duringdeposition, a lower chamber pressure, and/or a lesser amount of sourceRF power in order to produce a more tensile layer.

Any appropriate deposition process can be employed to deposit thedielectric layer having a desired stress level during step 220. In oneparticular embodiment, a flow of substantially inert gas is provided toform a plasma above substrate 90. As used herein, “substantially inertgas” refers to a gas or combination of gases that does not result inappreciable deposition during the deposition process. The substantiallyinert gas may be O₂, Ar, He, H₂, N₂, or a mixture of the previous gases.The specific substantially inert gas that is used is not critical to theprocess being described, meaning that a similar amount of Ar flow couldbe substituted for a comparable flow of He, or any other substantiallyinert gas may be used within this process.

Table 1 below lists the process parameters for deposition step 220 usedto create a low tensile stress film as compared to a conventionalHDP-CVD deposition parameters implemented in the Ultima HDP-CVD chambermanufactured for Applied Materials and outfitted for 200 mm substratesaccording to one particular embodiment of the invention. The gas flowrates and other parameters set forth in Table 1 below are optimized fora deposition process run in the Ultima chamber. A person of ordinaryskill in the art will recognize that these rates and parameters are inpart chamber specific and will vary if chambers of other design and/orvolume are employed.

TABLE 1 Exemplary Ranges for Process Parameters Conventional Low TensileStress Parameter Deposition Deposition Wafer Position process - waferchucked process - wafer chucked Step Duration 60 s-400 s 60 s-400 sChamber Pressure 4-20 mT <4 mT (1.0 mT-4 mT) Wafer Temperature 500-700deg C. <500 deg C. (200 C. to 300 C.) ESC Temp Setpoint 100-300 deg C.25-75 deg C. Top Source RF Power 3-5 kW 1-4 kW Side Source RF Power 3-5kW 1-4 kW Bias Voltage 1-4 Kw 1-4 kW Gas Flow SiH₄, O₂, H₂, inert gasSiH₄, O₂, H₂, inert gas Gas flow amounts SiH₄ 20-100 sccm SiH₄ 20-100sccm O₂ 30-150 sccm O₂ 30-150 sccm

After the completion of the deposition process of step 220, thesubstrate 90 is then moved to an elevated position in step 240 above thesubstrate receiving portion 19 by extending the lift pins 92. The plasmacreated during the deposition process 220 is still present above thesubstrate 90, and is maintained through the substrate movement step 240by continuing to flow inert gases. Process parameters for step 240 areshown in Table 2. A typical duration of the substrate movement step 240will last between 1-10 seconds. In an exemplary embodiment, thesubstrate 90 is lifted to the position 58, where the height that thelift pins 92 are extended may vary from 1 to 50 mm, so long as the backside of the substrate 90 is no longer in contact with the substratereceiving portion 19.

TABLE 2 Exemplary Ranges for Process Parameters During SubstrateParameter Movement Plasma Treatment Substrate Position substrate ismoving process position Step Duration 1-10 s 10-60 s Chamber Pressure 10mT 8-12 mT Substrate Temperature N/A >300 deg C. (400 C.-600 C.) ESCTemp Setpoint N/A N/A Top Source RF Power 1-3 kW 3-8 kW Side Source RFPower 1-3 kW 3-8 kW Bias Voltage N/A 0 kW Gas Flow none inert gas Gasflow Amounts O₂ 200 sccm O₂ 200 sccm Ar 50 sccm He(side) 460 sccm He(top) 500 sccm

The substrate 90 is now situated above the substrate receiving portion19 on the lift pins 92 for plasma treatment in step 250. Plasmatreatment of the substrate 90 in an elevated position induces a changein the stress of the deposited layer not seen when plasma treatment ofthe substrate occurs at a processing position. By raising the substrate90 to an elevated position above the substrate receiving portion 19,both the deposited layer on the top surface of the substrate 90 as wellas the bottom surface of the substrate 90 are exposed to the plasma. Theduration of exposure to the plasma is a period greater than 10 seconds,but optimally 30-60 seconds in step 250. Process parameters for step 250are shown within Table 2. The inventors have found that even if thedistance between the substrate 90 and substrate receiving portion 19 isonly 1 mm, the plasma present during step 250 will occupy the gapbetween the substrate 90 and substrate receiving portion 19 and treatboth the top and bottom sides of the substrate 90. While not beinglimited to any particular theory, this exposure of both the top andbottom surface of the substrate 90 causes a shift in the chemicalcomponent and phase of the deposited layer, as well as a change in thetemperature profile of both the deposited layer and substrate. Thiscontrasts with the use of plasma treatment at a non-elevated position,in which only the top surface of the deposited layer was exposed to theplasma treatment. Additionally, a greater amount of moisture contentpresent within the deposited layer is driven out by the plasma treatmentat an elevated position. Shrinkage of the deposited layer occurs, thuscausing the layer to become thinner and more dense as the excessmoisture is removed. The exposure of the deposited layer to plasma in anelevated position results in the stress of the layer increasing morethan 100 MPa in the tensile direction, meaning that a low compressivestress layer may be altered to exhibit a low tensile stress, or a lowtensile stress layer may be altered to exhibit a high tensile stress. Inparticular, changes of nearly 150 MPa in the stress of a deposited layerhave been exhibited after plasma treatment according to this invention.

Without being limited by an explanation, one possible reason that ahigher tensile stress layer can be formed by the exemplary plasmatreatment described herein is that a layer having higher stress valuescan be obtained by reducing the net hydrogen content, or the amount ofsilicon-hydrogen bonds (Si—H bonds) in the deposited layer. It isbelieved that lower hydrogen content in the deposited layer, whichresults in a detectably smaller amount of Si—H bonds in the as-depositedlayer, gives rise to higher tensile stress values in the depositedlayer. The use of a plasma treatment of a deposited layer on a substratecan be used to achieve lower hydrogen content in the deposited layer,and thus increase the tensile stress of the substrate.

At the conclusion of the plasma treatment process, the plasma isextinguished by stopping the flow of inert gas and the substrate 90 isreadied for output in step 270 by being raised to upper loading position57. The vertical position of the substrate 90 is changed by raising thelift pins 92 to allow a robot blade (not shown) to remove the substrate90 from the chamber.

Embodiments of the present invention can be implemented using a varietyof high density plasma CVD substrate processing chambers includingchambers in which a plasma is formed by the application of RF energy toa coil that at least partially surrounds a portion of the chamber andchambers that use ECR plasma formation techniques. An example of aninductively-coupled HDP-CVD chamber in which embodiments of the methodof the present invention can be practiced is set forth below.

FIG. 3A illustrates one embodiment of a high density plasma chemicalvapor deposition (HDP-CVD) system 110 in which a substrate can beprocessed according to the present invention. System 110 includes achamber 113, a vacuum system 170, a source plasma system 180A, a biasplasma system 180B, a gas delivery system 133, and a remote plasmacleaning system 150.

The upper portion of chamber 113 includes a dome 114, which is made of aceramic dielectric material, such as aluminum oxide or aluminum nitride.Dome 114 defines an upper boundary of a plasma processing region 116.Plasma processing region 116 is bounded on the bottom by the uppersurface of a substrate 117 and a substrate support member 118.

A heater plate 123 and a cold plate 124 surmount, and are thermallycoupled to, dome 114. Heater plate 123 and cold plate 124 allow controlof the dome temperature to within about +−10 degrees C. over a range ofabout 100 degrees C. to 200 degrees C. This allows optimizing the dometemperature for the various processes. For example, it may be desirableto maintain the dome at a higher temperature for cleaning or etchingprocesses than for deposition processes. Accurate control of the dometemperature also reduces the flake or particle counts in the chamber andimproves adhesion between the deposited layer and the substrate.

The lower portion of chamber 113 includes a body member 122, which joinsthe chamber to the vacuum system. A base portion 121 of substratesupport member 118 is mounted on, and forms a continuous inner surfacewith, body member 122. Substrates are transferred into and out ofchamber 113 by a robot blade (not shown) through an insertion/removalopening (not shown) in the side of chamber 113. Lift pins (shown in FIG.2) are raised and then lowered under the control of a motor (not shown)to move the substrate to different positions within the chamber 113. Thelift pins may be configured to move the substrate from the robot bladeat an upper loading position 57 to a position 58 where, as explainedfurther below, the substrate is prepared for processing. Subsequently,the lift pins may move the substrate to a lower processing position 56in which the substrate is placed on a substrate receiving portion 119 ofsubstrate support member 118. Substrate receiving portion 119 includesan electrostatic chuck 120 that secures the substrate to substratesupport member 118 during substrate processing. In a preferredembodiment, substrate support member 118 is made from an aluminum oxideor aluminum ceramic material.

Vacuum system 170 includes throttle body 125, which houses twin-bladethrottle valve 126 and is attached to gate valve 127 and turbo-molecularpump 128. It should be noted that throttle body 125 offers minimumobstruction to gas flow, and allows symmetric pumping. Gate valve 27 canisolate pump 128 from throttle body 125, and can also control chamberpressure by restricting the exhaust flow capacity when throttle valve126 is fully open. The arrangement of the throttle valve, gate valve,and turbo-molecular pump allow accurate and stable control of chamberpressures from between about 1 millitorr to about 2 torr.

The source plasma system 180A includes a top coil 129 and side coil 130,mounted on dome 114. A symmetrical ground shield (not shown) reduceselectrical coupling between the coils. Top coil 129 is powered by topsource RF (SRF) generator 131A, whereas side coil 130 is powered by sideSRF generator 131B, allowing independent power levels and frequencies ofoperation for each coil. This dual coil system allows control of theradial ion density in chamber 113, thereby improving plasma uniformity.Side coil 130 and top coil 129 are typically inductively driven, whichdoes not require a complimentary electrode. In a specific embodiment,the top source RF generator 131A provides up to 5,000 watts of RF powerat nominally 2 MHz and the side source RF generator 131B provides up to5,000 watts of RF power at nominally 2 MHz. The operating frequencies ofthe top and side RF generators may be offset from the nominal operatingfrequency (e.g. to 1.7-1.9 MHz and 1.9-2.1 MHz, respectively) to improveplasma-generation efficiency.

A bias plasma system 180B includes a bias RF (“BRF”) generator 131C anda bias matching network 132C. The bias plasma system 180B capacitivelycouples substrate portion 117 to body member 122, which act ascomplimentary electrodes. The bias plasma system 180B serves to enhancethe transport of plasma species (e.g., ions) created by the sourceplasma system 180A to the surface of the substrate. In a specificembodiment, bias RF generator provides up to 5,000 watts of RF power at13.56 MHz.

RF generators 131A and 131B include digitally controlled synthesizersand operate over a frequency range between about 1.8 to about 2.1 MHz.Each generator includes an RF control circuit (not shown) that measuresreflected power from the chamber and coil back to the generator andadjusts the frequency of operation to obtain the lowest reflected power,as understood by a person of ordinary skill in the art. RF generatorsare typically designed to operate into a load with a characteristicimpedance of 50 ohms. RF power may be reflected from loads that have adifferent characteristic impedance than the generator. This can reducepower transferred to the load. Additionally, power reflected from theload back to the generator may overload and damage the generator.Because the impedance of a plasma may range from less than 5 ohms toover 900 ohms, depending on the plasma ion density, among other factors,and because reflected power may be a function of frequency, adjustingthe generator frequency according to the reflected power increases thepower transferred from the RF generator to the plasma and protects thegenerator. Another way to reduce reflected power and improve efficiencyis with a matching network.

Matching networks 132A and 132B match the output impedance of generators131A and 131B with their respective coils 129 and 130. The RF controlcircuit may tune both matching networks by changing the value ofcapacitors within the matching networks to match the generator to theload as the load changes. The RF control circuit may tune a matchingnetwork when the power reflected from the load back to the generatorexceeds a certain limit. One way to provide a constant match, andeffectively disable the RF control circuit from tuning the matchingnetwork, is to set the reflected power limit above any expected value ofreflected power. This may help stabilize a plasma under some conditionsby holding the matching network constant at its most recent condition.

Other measures may also help stabilize a plasma. For example, the RFcontrol circuit can be used to determine the power delivered to the load(plasma) and may increase or decrease the generator output power to keepthe delivered power substantially constant during deposition of a layer.

A gas delivery system 133 provides gases from several sources 134A-134Eto the chamber for processing the substrate via gas delivery lines 138(only some of which are shown). As would be understood by a person ofskill in the art, the actual sources used for sources 134A-134E and theactual connection of delivery lines 138 to chamber 113 varies dependingon the deposition and cleaning processes executed within chamber 113.Gases are introduced into chamber 113 through a gas ring 137 and/or atop nozzle 145. FIG. 3B is a simplified, partial cross-sectional view ofchamber 113 showing additional details of gas ring 137.

In one embodiment, first and second gas sources, 134A and 134B, andfirst and second gas flow controllers, 135A′ and 135B′, provide gas toring plenum 136 in gas ring 137 via gas delivery lines 138 (only some ofwhich are shown). Gas ring 137 has a plurality of source gas nozzles 139(only one of which is shown for purposes of illustration) that provide auniform flow of gas over the substrate. Nozzle length and nozzle anglemay be changed to allow tailoring of the uniformity profile and gasutilization efficiency for a particular process within an individualchamber. In a preferred embodiment, gas ring 137 has 12 source gasnozzles made from an aluminum oxide ceramic.

Gas ring 137 also has a plurality of oxidizer gas nozzles 140 (only oneof which is shown), which in a preferred embodiment are co-planar withand shorter than source gas nozzles 139, and in one embodiment receivegas from body plenum 141. In some embodiments it is desirable not to mixsource gases and oxidizer gases before injecting the gases into chamber113. In other embodiments, oxidizer gas and source gas may be mixedprior to injecting the gases into chamber 113 by providing apertures(not shown) between body plenum 141 and gas ring plenum 136. In oneembodiment, third and fourth gas sources, 134C and 134D, and third andfourth gas flow controllers, 135C and 135D′, provide gas to body plenumvia gas delivery lines 138. Additional valves, such as 143B (othervalves not shown), may shut off gas from the flow controllers to thechamber.

In embodiments where flammable, toxic, or corrosive gases are used, itmay be desirable to eliminate gas remaining in the gas delivery linesafter a deposition.

This may be accomplished using a 3-way valve, such as valve 143B, toisolate chamber 113 from delivery line 138A and to vent delivery line138A to vacuum foreline 144, for example. As shown in FIG. 3A, othersimilar valves, such as 143A and 143C, may be incorporated on other gasdelivery lines. Such 3-way valves may be placed as close to chamber 113as practical, to minimize the volume of the unvented gas delivery line(between the 3-way valve and the chamber). Additionally, two-way(on-off) valves (not shown) may be placed between a mass flow controller(“MFC”) and the chamber or between a gas source and an MFC.

Referring again to FIG. 3A, chamber 113 also has top nozzle 145 and topvent 146. Top nozzle 145 and top vent 146 allow independent control oftop and side flows of the gases, which improves layer uniformity andallows fine adjustment of the layer's deposition and doping parameters.Top vent 146 is an annular opening around top nozzle 145. In oneembodiment, first gas source 134A supplies source gas nozzles 139 andtop nozzle 145. Source nozzle MFC 135A′ controls the amount of gasdelivered to source gas nozzles 139 and top nozzle MFC 135A controls theamount of gas delivered to top gas nozzle 145. Similarly, two MFCs 135Band 135B′ may be used to control the flow of oxygen to both top vent 146and oxidizer gas nozzles 140 from a single source of oxygen, such assource 134B. The gases supplied to top nozzle 145 and top vent 146 maybe kept separate prior to flowing the gases into chamber 113, or thegases may be mixed in top plenum 148 before they flow into chamber 113.Separate sources of the same gas may be used to supply various portionsof the chamber.

A remote microwave-generated plasma cleaning system 150 is provided toperiodically clean deposition residues from chamber components. Thecleaning system includes a remote microwave generator 151 that creates aplasma from a cleaning gas source 134E (e.g., molecular fluorine,nitrogen trifluoride, other fluorocarbons or equivalents) in reactorcavity 153. The reactive species resulting from this plasma are conveyedto chamber 113 through cleaning gas feed port 154 via applicator tube155. The materials used to contain the cleaning plasma (e.g., cavity 153and applicator tube 155) must be resistant to attack by the plasma. Thedistance between reactor cavity 153 and feed port 154 should be kept asshort as practical, since the concentration of desirable plasma speciesmay decline with distance from reactor cavity 153. Generating thecleaning plasma in a remote cavity allows the use of an efficientmicrowave generator and does not subject chamber components to thetemperature, radiation, or bombardment of the glow discharge that may bepresent in a plasma formed in situ. Consequently, relatively sensitivecomponents, such as electrostatic chuck 120, do not need to be coveredwith a dummy wafer or otherwise protected, as may be required with an insitu plasma cleaning process. In one embodiment, this cleaning system isused to dissociate atoms of the etchant gas remotely, which are thensupplied to the process chamber 113. In another embodiment, the etchantgas is provided directly to the process chamber 113. In still a furtherembodiment, multiple process chambers are used, with deposition andetching steps being performed in separate chambers.

System controller 160 controls the operation of system 110. In apreferred embodiment, controller 160 includes a memory 162, such as ahard disk drive, a floppy disk drive (not shown), and a card rack (notshown) coupled to a processor 161. The card rack may contain asingle-board computer (SBC) (not shown), analog and digital input/outputboards (not shown), interface boards (not shown), and stepper motorcontroller boards (not shown). The system controller conforms to theVersa Modular European (“VME”) standard, which defines board, card cage,and connector dimensions and types. The VME standard also defines thebus structure as having a 16-bit data bus and 24-bit address bus. Systemcontroller 160 operates under the control of a computer program storedon the hard disk drive or through other computer programs, such asprograms stored on a removable disk. The computer program dictates, forexample, the timing, mixture of gases, RF power levels and otherparameters of a particular process.

In an alternate embodiment of the invention shown in FIG. 4, a sputterstep 230 may be performed after the completion of the deposition step220 while the substrate 90 is still at the processing position 56. Steps200-220 are performed in accordance with the description of those stepsfor FIG. 1. The plasma formed within the previous deposition step 220 ismaintained by continuing to flow a substantially inert gas while alsoproviding RF power through the top coil 129 and side coils 130. Gaseousions within the plasma are attracted towards the biased substratereceiving portion 119 and bombard the deposited layer on the substrate,thus raising the temperature of the substrate 90 to a temperature ofbetween 400-700 degrees C. This temperature increase occurs primarilydue to heat transfer from the charged plasma ions impacting thedeposited layer on top of the substrate 90. A small amount of thedeposited material may be etched away during the sputter process, butthe amount is minimal and may be compensated for by adjusting thedeposition recipe. The pressure during the sputter step is maintained asa stable pressure, with an exemplary chamber pressure existing between 5to 9 mT. The duration of the sputter step 230 in an exemplary embodimentis between 15 and 45 seconds. Exemplary process parameters for steps220-260 of the invention are shown in Table 3.

TABLE 3 Exemplary Ranges for Process Parameters During During SubstratePlasma Parameter Deposition Sputtering Movement Treatment SubstratePosition process - process substrate is lift position substrate movingchucked Step Duration 60 s-400 s 15-45 s 1-10 s 15-45 s Chamber Pressure<4 mT (1.0 mT-4 mT) 5-9 mT 10 mT 5-9 mT Substrate <500 deg C. 400 C.-700C. N/A >300 deg C. Temperature (200 C. to 300 C.) (400 C.-600 C.) ESCTemp setpoint 25-75 deg C. 25-75 deg C. N/A N/A Top Source RF 1-4 kW 1-3kW 1-3 kW 1-3 kW Power Side Source RF 1-4 kW 1-3 kW 1-3 kW 1-3 kW PowerBias Voltage 1-4 kW 3.5 kW N/A N/A Gas Flow SiH₄, O₂, H₂, inert gasinert gas inert gas inert gas Gas flow Amounts SiH₂ 20-100 sccm O₂ 20sccm O₂ 200 sccm O₂ 200 sccm O₂ 30-150 sccm He (side) 460 sccm He (side)460 sccm He (top) 460 sccm He (top) 460 sccm

After the sputter step 230 is complete, the plasma present duringsputtering is maintained throughout the movement of the substrate 90 toan elevated position in step 240. Due to the added sputter step 230, thesubstrate temperature has already been raised to a higher temperatureand the process parameters for plasma treatment step after sputtering260 can be different than if performed without a sputter step 230. Forexample, while the process conditions are similar to that of plasmatreatment step 250 performed without a sputter step, a shorter durationof between 15-45 seconds may be utilized in plasma treatment aftersputtering 260, along with a chamber pressure of 5-9 mT. Additionally,in one embodiment the amount of RF power delivered to the top 129 andside coils 130 delivered is a reduced amount of 1-3 kW. The substrate isthen readied for output in step 270.

In an alternate embodiment of the invention, a two-step plasma treatmentprocess is used to treat the substrate 90, as shown in FIG. 5. Thesubstrate is placed within the chamber, moved to process position 56,and a dielectric layer is deposited as in steps 200-220. Following thedeposition of a dielectric layer on a substrate 90 in step 220, theplasma created in step 220 is maintained while the substrate 90 is keptat processing position 56 to treat the substrate 90 with a plasma for aduration of at least 10 seconds in step 330. The process conditions ofstep 330 are similar to those used in step 250, except that the durationof the plasma treatment at the process position may be shorter due tothe two-step nature of the plasma treatment. The process parameters forthe two-step plasma treatment process are shown in Table 4.Subsequently, the substrate is lifted to an elevated position above thesubstrate receiving position 119 in step 240 and both the depositedlayer and bottom of the substrate 90 are then exposed to a plasma instep 350 for a duration between 10-40 seconds at a pressure of between8-12 mT. A reduced amount of RF power is applied to the top 129 and side130 RF coils of between 1-4 kW is used to maintain the plasma. Thetemperature of the substrate is maintained at a temperature between300-600 degrees C., and gas flows of 300-600 sccm He to both the sidesource 139 and top 145 nozzles are provided, in addition to gas flows of100-300 sccm O₂ and 25-100 sccm Ar. This approach can also yield atensile stress of 100 MPa greater than the original stress of thesubstrate prior to treatment. The substrate is then readied for outputin step 270.

TABLE 4 Exemplary Ranges for Process Parameters During SubstrateParameter During Deposition Plasma Treatment Movement Plasma TreatmentSubstrate process - substrate process position substrate is liftposition Position chucked moving Step Duration 60 s-400 s 10-40 s 1-10 s10-40 s Chamber <4 mT (1.0 mT-4 mT) 8-12 mT 8-12 mT 8-12 mT PressureSubstrate <500 deg C. >300 deg C. 1-3 kW >300 deg C. Temperature (200 C.to 300 C.) (400 C.-600 C.) (400 C.-600 C.) ESC Temp 25-75 deg C. N/A 1-3kW N/A setpoint Top Source RF 1-4 kW 3-8 kW 2 kW 1-4 kW Power SideSource RF 1-4 kW 3-8 kW 2 kW 1-4 kW Power Bias Voltage 1-4 kW 0 Kw N/A 0kW Gas Flow SiH₄, O₂, H₂, inert inert gas none inert gas gas Gas flowSiH₄ 20-100 sccm O₂ 200 sccm O₂ 200 sccm O₂ 200 sccm Amounts O₂ 30-150sccm Ar 50 sccm Ar 50 sccm He(side) 460 sccm He(side) 460 sccm He (top)460 sccm He (top) 460 sccm

In another embodiment of the invention, a discontinuous plasma treatmentis used to treat the substrate 90 following the deposition process.After a dielectric layer has been deposited on the substrate, the plasmacreated during deposition is maintained for a period of time while thesubstrate 90 is still positioned on the substrate receiving portion 119at processing position 56. In this particular embodiment, the period oftime that the substrate is exposed to plasma is a period between 30-60seconds, but may also be longer or shorter depending on the type ofdielectric being deposited. Following the initial plasma treatment, theplasma is turned off by stopping the flow of gases into the chamber. Thesubstrate is then moved to a lift position 58 during a substratemovement step 240 by raising lift pins 92 to a height above thesubstrate receiving portion 19. A plasma is then reformed by flowinginert gases into the chamber and applying RF energy through the side andtop coils. The plasma treats both the top and bottom sides of theelevated substrate, thus changing the stress of the wafer to become moretensile.

The techniques described in various embodiments of the current inventioncan be advantageously used within many different process applications,such as a shallow trench isolation (STI) application. The use of aplasma treatment within an STI application is shown in FIGS. 6A-6E anddescribed in more detail below. Several of the steps may occur within aseries of different chambers, but the deposition of the dielectric layerand plasma treatment process occur within one chamber.

A thin pad oxide 402 is first grown or deposited on a silicon substrate400, and a nitride layer 404 is deposited over the layer of pad oxide402, as shown in FIG. 6A. The nitride layer 404 is used as an etch-stoplayer and acts as a hard mask for the trench etch steps. Followingdeposition, a lithography process is implemented to form a photoresistmask and pattern a trench opening 406 in the pad oxide and nitridelayers, shown in FIG. 6B. A nitride etch and silicon etch are used tocreate a deep trench 408 within the silicon. This is shown in FIG. 6C.After removal of the photoresist mask, the substrate 400 is then movedto a substrate processing chamber 13 and moved into a processingposition 56. A dielectric layer 410 is then deposited on the substrate400, filling both the trench region and mesa regions adjacent to thetrench 408. The result of the dielectric deposition process is shown inFIG. 6D. The substrate 400 is then raised by a lifting mechanism such aslift pins to an elevated position. The plasma created during depositionis maintained throughout this process. The substrate 400 is then exposedto the plasma for a given duration, affecting both the top and bottom ofthe substrate. After extinguishing the plasma, the substrate is readiedfor output from the chamber. Process conditions for the plasma treatmentstep can be found in Tables 1 and 2. Following the plasma treatmentprocess, a CMP process is used to remove excess portions of thedielectric layer 410 formed during the deposition step as shown in FIG.6E. Following the removal of portions of the dielectric layer, a nitrideand pad oxide strip is used to remove the nitride 404 and pad oxidelayers 402 from the trench, as shown in FIG. 6E. This leaves the trench408 filled with a dielectric material 410 with a silicon area presentbetween adjacent trenches that can be used for transistor formation. Inan alternative process flow, a sputter step can also be incorporatedafter deposition whereby plasma ions are attracted to the biasedsubstrate.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. In particular, while embodiments have been described indetail for high-density plasma system, those of skill in the art willrecognize the general applicability of the invention to any substrateprocessing system that uses a plasma to treat the substrate. Forexample, while the invention described with respect to an undopedsilicate glass layer, the invention can also be used to improve thetensile stress of phosphosilicate glass (PSG), boron-doped silicateglass (BSG), boron phosphosilicate glass (BPSG) layers andfluorine-doped silicon glass (FSG) as well as other types of materials.Also, in other embodiments, silicon sources other than monosilane may beused. Examples of suitable silicon sources include other silane familymembers such as, Si₂H₆, Si₃H₈, etc.; TEOS and SiF₄ among others. Assuch, the above description is illustrative and not restrictive. Aperson of ordinary skill in the art will recognize that the exemplaryranges and process parameters described herein are experimentallydetermined and further modifications to these values may be possiblewith further experimentation. Accordingly, the above description shouldnot be taken as limiting the scope of the invention, which is defined inthe following claims.

1. A method of forming a dielectric layer comprising: placing asubstrate on a substrate support in a chamber, and while the substrateis in the chamber; depositing a dielectric layer on the substrate usinga plasma deposition process; while maintaining plasma created during theplasma deposition process, raising the substrate above the substratesupport; and while the substrate is raised above the substrate support,exposing the substrate to plasma treatment that increases the tensilestress of the deposited layer.
 2. The method of claim 1 wherein thedielectric layer when deposited has a stress of less than 100 MPacompressive stress.
 3. The method of claim 2 wherein the increase intensile stress of the deposited layer is at least 100 MPa.
 4. The methodof claim 1 further comprising after depositing the dielectric layer andprior to raising the substrate, exposing the substrate to a sputteringprocess that increases the substrate temperature.
 5. The method of claim4 wherein a plasma is continuously maintained between the step ofexposing the substrate to a sputtering process and exposing thesubstrate to plasma treatment that increases the tensile stress of thedeposited layer.
 6. The method of claim 1 further comprising afterdepositing the dielectric layer and prior to raising the substrate,exposing the substrate to an initial plasma treatment while the backsurface of the substrate is still in contact with the substrate support.7. The method of claim 1 wherein the plasma treatment ionizes a gaswhich is O₂, Ar, He, H₂, N₂, or a mixture of the gases listed.
 8. Themethod of claim 1 wherein the deposited layer has a first stress whichis compressive, and after exposure to plasma treatment, has a secondstress which is tensile.
 9. The method of claim 1 wherein the depositedlayer has a first stress which is tensile, and after exposure to plasmatreatment, has a second stress which is more tensile than the firststress.
 10. The method of claim 1 wherein the substrate is raised abovethe substrate support by a plurality of lift pins that extend the liftpins through the substrate support.
 11. The method of claim 1 whereinthe substrate and layer are heated to a temperature greater than 300degrees Celsius a result of exposure to the plasma treatment.
 12. Themethod of claim 1 wherein the substrate is raised to a height of between1 to 50 mm above the substrate support during the raising step.
 13. Themethod of claim 1 wherein the substrate is exposed to the plasma for aperiod of 10-60 seconds during the exposing step.
 14. The method ofclaim 1 wherein the plasma is a high-density plasma.
 15. The method ofclaim 1 wherein the dielectric layer is a layer of undoped siliconglass.
 16. The method of claim 1 wherein the chamber pressure during theplasma treatment of the substrate is less than 15 mT.
 17. A method offorming a dielectric layer on a substrate disposed on a substratesupport in a substrate processing chamber, comprising: placing thesubstrate in the chamber; positioning the substrate on a surface of thesubstrate support; while the substrate is positioned on the surface ofthe substrate support, depositing the dielectric layer over thesubstrate using a plasma deposition process, wherein the depositeddielectric layer has a first stress as a result of deposition; whilemaintaining plasma created during the plasma deposition process, raisingthe substrate above the surface of the substrate support to an elevatedposition; and in the elevated position, exposing a top and bottomsurface of the substrate to the plasma whereby the stress of thedielectric layer is increased to a second stress more tensile than thefirst stress.
 18. A method of forming a dielectric layer on a substratecomprising: placing the substrate on a first surface of a substratesupport in a substrate processing chamber; depositing the dielectriclayer over the substrate on the first surface of the substrate supportusing a high density plasma CVD deposition process, wherein thedielectric layer has a first stress less than or equal to 100 MPacompressive as a result of deposition; exposing the substrate on thefirst surface of the substrate support to a high density plasma whilebiasing the substrate, wherein the high density plasma consists ofsubstantially inert gas and exposure to the high density plasmaincreases a temperature of the substrate to between about 400-700° C.;thereafter raising the substrate above the first surface of thesubstrate support; and while the substrate is raised above the firstsurface of the substrate support, exposing the substrate to a secondhigh density plasma, wherein the stress of the dielectric layer isincreased to a second stress that is at least 100 MPa more tensile thanthe first stress.
 19. The method of claim 18 wherein said step ofraising the substrate is done by extending lift pins through thesubstrate support to a height of at least 1 mm and the substrate isexposed to the second high density plasma for a period between 10-60seconds.
 20. The method of claim 18 wherein plasma is maintained betweenthe exposing step steps.
 21. The method of claim 18 wherein the firststress is between 0-50 MPa compressive and the second stress is between100-200 MPa tensile.
 22. The method of claim 20 wherein first stress isbetween 0-50 MPa tensile and the second stress is between 100-200 MPatensile.
 23. The method of claim 20 wherein the first stress is between0-50 MPa compressive and the second stress is between 0-140 MPa tensile.24. The method of claim 1 wherein the deposited layer has a first stressand after exposure to plasma treatment has a second stress that is moretensile than the first stress.